Percutaneous nephroscopy is being used increasingly for kidney treatment, especially for the extraction of kidney stones. Nephroscopy differs from conventional kidney surgery in that an endoscope is inserted through the skin and the tissue just beneath the skin into the kidney to perform the necessary procedure.
Before the endoscope can be inserted, an insertion canal must be created for it. This canal must be precisely positioned and must be created from the skin to the renal calyx through the tissue between the skin and the kidney as well as through the parenchyma of the kidney. A two-stage procedure is therefore used to create the canal. First, a guide wire is installed by passing it through the skin and other tissues, directing the wire with real-time observation using techniques such as X-rays and sonograms.
This kind of small-diameter canal can be formed with precision and substantially without risk. However, the passage thus formed is somewhat too small for an endoscope which can have a diameter several times larger than the wire. Thus, it is necessary to expand the canal with some form of device which can be installed on the wire, enlarging it to a size which corresponds to that of the endoscope.
In accordance with the current state of the art, dilators are used to enlarge the insertion canal by being pushed through the canal. One such dilator is described in U.S. Pat. No. 4,449,532, Storz. That device expands the canal in stages, using a series of telescopically related members of increasing diameters.
The disadvantages involved in the current state of the art arise from the process of dilating the initially narrow canal to the somewhat larger diameter of the endoscope. The initially created canal made by the wire has a diameter of perhaps 2 mm. but the endoscope may have a diameter of 10 mm., for example. This very significant expansion is the basic reason for the multiple stages of enlargement, but the technique is not totally satisfactory.
Because of the great enlargement, considerable force must be used to push the device into the patient. As a result, there is a considerable risk of undesired erroneous movements with the concomitant danger of injury. Furthermore, expansion to this extent in multiple stages requires a considerable amount of time to the discomfort of the patient. The patient particularly experiences considerable pain in procedures done under local anesthesia. Also, because of the multiple stages, the painful areas of tissue are repeatedly irritated.
Problems also arise at certain tissue points such as, for example, at hard, difficult-to-penetrate muscle tissue, at hardened muscles or when scar tissue from previous surgery is required to stretch.